I don't think it's a problem technically, but you might want to check to see if it is actually legal. I was thinking of doing the same thing, but most of the reputable places state that the xenon kits they sell are for off-road use only. You may "get away" with a 4300k kit because they'll be the closest to a factory brightness.
Check out this place:
http://www.brightheadlights-hid.com/Xenon-HID-Lights-Kits.htm
They do state that they have a street legal kit, but they are actually auxillary driving lights, not the complete conversion kit for your headlights.
The legality lies in the housing itself. That's why they sell the entire housings from the factory for the kits. I've read the legal notice on these kits and that's where the problems lie. Personally, I don't think anyone will give you a second look driving a Porsche.